Multiple transform utilization and applications for secure digital watermarking

ABSTRACT

Multiple transform utilization and applications for secure digital watermarking. In one embodiment of the present invention, digital blocks in digital information to be protected are transformed into the frequency domain using a fast Fourier transform. A plurality of frequencies and associated amplitudes are identified for each of the transformed digital blocks and a subset of the identified amplitudes is selected for each of the digital blocks using a primary mask from a key. Message information is selected from a message using a transformation table generated with a convolution mask. The chosen message information is encoded into each of the transformed digital blocks by altering the selected amplitudes based on the selected message information.

FIELD OF THE INVENTION

[0001] The invention relates to the protection of digital information.More particularly, the invention relates to multiple transformutilization and applications for secure digital watermarking.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. patent applicationSer. No. 08/587,943, filed Jan. 17, 1996, entitled “Method forStega-Cipher Protection of Computer Code,” the entire disclosure ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0003] Increasingly, commercially valuable information is being createdand stored in “digital” form. For example, music, photographs and videocan all be stored and transmitted as a series of numbers, such as 1'sand 0's. Digital techniques let the original information be recreated ina very accurate manner. Unfortunately, digital techniques also let theinformation be easily copied without the owner's permission.

[0004] Digital watermarks exist at a convergence point where creatorsand publishers of digitized multimedia content demand local, secureidentification and authentication of content. Because piracy discouragesthe distribution of valuable digital information, establishingresponsibility for copies and derivative copies of such works isimportant. The goal of a digital watermark system is to insert a giveninformation signal or signals in such a manner as to leave little or noartifacts, with one standard being perceptibility, in the underlyingcontent signal, while maximizing its encoding level and “locationsensitivity” in the signal to force damage to the content signal whenremoval is attempted. In considering the various forms of multimediacontent, whether “master,” stereo, National Television StandardsCommittee (NTSC) video, audio tape or compact disc, tolerance of qualitywill vary with individuals and affect the underlying commercial andaesthetic value of the content. It is desirable to tie copyrights,ownership rights, purchaser information or some combination of these andrelated data into the content in such a manner that the contentundergoes damage, and therefore reduction of its value, with subsequentunauthorized distribution, commercial or otherwise. Digital watermarksaddress many of these concerns and research in the field has provided arich basis for extremely robust and secure implementations.

[0005] Of particular concern is the balance between the value of adigitized “piece” of content and the cost of providing worthwhile“protection” of that content. In a parallel to real world economicbehavior, the perceived security of a commercial bank does not causepeople to immediately deposit cash because of the expense and timerequired to perform a bank deposit. For most individuals, possession ofa US$100 bill does not require any protection beyond putting it into awallet. The existence of the World Wide Web, or “Web,” does notimplicitly indicate that value has been created for media which can bedigitized, such as audio, still images and other media. The Web issimply a medium for information exchange, not a determinant for thecommercial value of content. The Web's use to exchange media does,however, provide information that helps determine this value, which iswhy responsibility over digitized content is desirable. Note thatdigital watermarks are a tool in this process, but they no not replaceother mechanisms for establishing more public issues of ownership, suchas copyrights. Digital watermarks, for example, do not replace the“historical average” approach to value content. That is, a market ofindividuals willing to make a purchase based solely on the perceivedvalue of the content. By way of example, a picture distributed over theInternet, or any other electronic exchange, does not necessarilyincrease the underlying value of the picture, but the opportunity toreach a greater audience by this form of “broadcast” may be a desirablemechanism to create “potentially” greater market-based valuations. Thatdecision rests solely with the rights holder in question.

[0006] Indeed, in many cases, depending on the time value of thecontent, value may actually be reduced if access is not properlycontrolled. With a magazine sold on a monthly basis, it is difficult toassess the value of pictures in the magazine beyond the time themagazine is sold. Compact disc valuations similarly have time-basedvariables, as well as tangible variables such as packaging versus thepackage-less electronic exchange of the digitized audio signals. TheInternet only provides a means to more quickly reach consumers and doesnot replace the otherwise “market-based” value. Digital watermarks,properly implemented, add a necessary layer of ownership determinationwhich will greatly assist in determining and assessing value when theyare “provably secure.” The present invention improves digitalwatermarking technology while offering a means to properly “tamperproof” digitized content in a manner analogous to methods forestablishing authenticity of real world goods.

[0007] A general weakness in digital watermark technology relatesdirectly to the way watermarks are implemented. Too many approachesleave detection and decode control with the implementing party of thedigital watermark, not the creator of the work to be protected. Thisfundamental aspect of various watermark technologies removes propereconomic incentives for improvement of the technology when third partiessuccessfully exploit the implementation. One specific form ofexploitation obscures subsequent watermark detection. Others regardsuccessful over encoding using the same watermarking process at asubsequent time.

[0008] A set of secure digital watermark implementations address thisfundamental control issue, forming the basis of “key-based” approaches.These are covered by the following patents and pending applications, theentire disclosures of which are hereby incorporated by reference: U.S.Pat. No. 5,613,004 entitled “Steganographic Method and Device” and itsderivative U.S. patent application Ser. No. 08/775,216, U.S. patentapplication Ser. No. 08/587,944 entitled “Human Assisted Random KeyGeneration and Application for Digital Watermark System,” U.S. patentapplication Ser. No. 08/587,943 entitled “Method for Stega-CipherProtection of Computer Code,” U.S. patent application Ser. No.08/677,435 entitled “Optimization Methods for the Insertion, Protection,and Detection of Digital Watermarks in Digitized Data,” and U.S. patentapplication Ser. No. 08/772,222 entitled “Z-Transform Implementation ofDigital Watermarks.” Public key crypto-systems are described in U.S.Pat. Nos. 4,200,770, 4,218,582, 4,405,829 and 4,424,414, the entiredisclosures of which are also hereby incorporated by reference.

[0009] By way of improving these digital watermark security methods,utilization of multiple transforms, manipulation of signalcharacteristics and the requisite relationship to the mask set or “key”used for encoding and decoding operations are envisioned, as areoptimized combinations of these methods. While encoding a watermark mayultimately differ only slightly in terms of the transforms used in theencoding algorithm, the greater issues of an open, distributedarchitecture requires more robust approaches to survive attempts aterasure, or even means for making detection of the watermark impossible.These “attacks,” when computationally compared, may be diametricallyrelated. For instance, cropping and scaling differ in signal processingorientation, and can result in the weakening of a particularwatermarking approach but not all watermarking approaches.

[0010] Currently available approaches that encode using either ablock-based or entire data set transform necessarily encode data ineither the spatial or frequency domains, but never both domains. Asimultaneous crop and scale affects the spatial and frequency domainsenough to obscure most available watermark systems. The ability tosurvive multiple manipulations is an obvious benefit to those seeking toensure the security of their watermarked media. The present inventionseeks to improve on key-based approaches to watermarking previouslydisclosed, while offering greater control of the subsequentlywatermarked content to rights owners and content creators.

[0011] Many currently available still image watermarking applicationsare fundamentally different from the key-based implementations. Suchproducts include products offered by Digimarc and Signum, which seek toprovide a robust watermark by encoding watermark messages that relyentirely on comparisons with the original image for decode operations.The subsequent result of the transform, a discrete cosine transformperformed in blocks, is digital signed. The embedded watermarks lack anyrelationship to the perceptual qualities of the image, making inverseapplication of the publicly available decoders a very good first line ofattack. Similarly, the encoding process may be applied by third parties,as demonstrated by some robustness tests, using one process to encodeover the result of an image watermarked with another process.Nonrepudiation of the watermark is not possible, because Digimarc andSignum act as the repository of all registrations of the image'sownership.

[0012] Another line of attack is a low pass filter that removes some ofthe high frequency noise that has been added, making error-freedetection difficult or impossible. Finally, many tests of a simple JPEGtransform indicate the watermarks may not survive as JPEG is based onthe same transforms as the encoding transforms used by the watermarkingprocess. Other notable implementations, such as that offered by Signafy(developed by NEC researchers), appear to encode watermark messages byperforming a transform of the entire image. The goal of this process isto more consistently identify “candidate” watermark bits or regions ofthe image to encode in perceptually significant regions of the signal.Even so, Signafy relies on the original unwatermarked image toaccomplish decoding.

[0013] All of these methods still rely on the original unwatermarkedimage to ensure relatively error-free detection of the watermarks. Thesteganographic method seeks to provide watermark security without anoriginal unwatermarked copy of the media for decode operations, as wellas providing users cryptographic security with ciphered symmetric keys.That is, the same key is used for encode and decode operations. Publickey pairs, where each user has a public/private key pair to performasymmetric encode and decode operations, can also be used. Discussionsof public key encryption and the benefits related to encryption are welldocumented. The growing availability of a public key infrastructure alsoindicates recognition of provable security. With such key-basedimplementations of watermarking, security can be off-loaded to the key,providing for a layered approach to security and authentication of thewatermark message as well as the watermarked content.

[0014] It is known that attacks on the survivability of otherimplementations are readily available. Interesting network-based attackson the watermark message are also known which fool the centralregistration server into assuming an image is owned by someone otherthan the registered owner. This also substantiates the concern thatcentralized watermarking technologies are not robust enough to provideproper assurances as to the ownership of a given digitized copy of anmultimedia work.

[0015] Because the computational requirements of performing multipletransforms may not be prohibitive for certain media types, such as stillimages and audio, the present invention seeks to provide a means tosecurely watermark media without the need for an original unwatermarkedcopy to perform decoding. These transforms may be performed in a mannernot plainly evident to observers or the owner of the content, who mayassume the watermark is still detectable. Additionally, where aparticular media type is commonly compressed (JPEG, MPEG, etc.),multiple transforms may be used to properly set the mask sets, prior tothe watermarking process, to alert a user to survivability prior to therelease of a watermarked, and thus perceived, “safe” copy to unknownparties. The result of the present invention is a more realisticapproach to watermarking taking the media type, as well as the provablesecurity of the keys into consideration. A more trusted model forelectronic commerce is therefore possible.

[0016] The creation of an optimized “envelope” for insertion ofwatermarks to establish secured responsibility for digitally-sampledcontent provides the basis of much watermark security but is also acomplementary goal of the present invention. The predetermined or randomkey that is generated is not only an essential map to access the hiddeninformation signal, but is also the a subset of the original signalmaking direct comparisons with the original signal unnecessary. Thisincreases the overall security of the digital watermark.

[0017] Survival of simultaneous cropping and scaling is a difficult taskwith image and audio watermarking, where such transformations are commonwith the inadvertent use of images and audio, and with intentionalattacks on the watermark. The corresponding effects in audio are farmore obvious, although watermarks which are strictly “frequency-based,”such as variations of spread spectrum, suffer from alignment issues inaudio samples which have been “cropped,” or clipped from the originallength of the piece. Scaling is far more noticeable to the humanauditory system, though slight changes may affect frequency-only-typewatermarks while not being apparent to a consumer. The far greaterthreat to available audio watermark applications, most of which arevariations of frequency-based embedded signaling, are generallytime-based transformations, including time-based compression andexpansion of the audio signal. Signafy is an example of spreadspectrum-based watermarking, as are applications by Solana Technology,CRL, BBN, MIT, etc. “Spatial domain” approaches are more appropriatedesignations for the technologies deployed by Digimarc, Signum, ARIS,Arbitron, etc. Interestingly, a time-based approached when consideredfor images is basically a “spatial-based” approach. The pixels are“convolutional.” The difference being that the “spread spectrum-ed” areaof the frequencies is “too” well-defined and thus susceptible toover-encoding of random noise at the same sub-bands as that of theembedded signal.

[0018] Giovanni uses a block-based approach for the actual watermark.However, it is accompanied by image-recognition capable of restoring ascaled image to its original scale. This “de-scaling” is applied beforethe image is decoded. Other systems used a “differencing” of theoriginal image with the watermarked image to “de-scale.” It is clearthat de-scaling is inherently important to the survival of any image,audio or video watermark. What is not clear is that the differencingoperation is acceptable from a security standpoint. Moreover,differencing that must be carried out by the watermarking “authority,”instead of the user or creator of the image, causes the rights owner tolose control over the original unwatermarked content. Aside fromutilizing the mask set within the encoding/decoding key/key pair, theoriginal signal must be used. The original is necessary to performdetection and decoding, although with the attacks described above it isnot possible to clearly establish ownership over the watermarkedcontent.

[0019] In view of the foregoing, it can be appreciated that asubstantial need exists for multiple transform utilization andapplications for secure digital watermarking that solve the problemsdiscussed above.

SUMMARY OF THE INVENTION

[0020] The disadvantages of the art are alleviated to a great extent bymultiple transform utilization and applications for secure digitalwatermarking. In one embodiment of the present invention, digital blocksin digital information to be protected are transformed into thefrequency domain using a fast Fourier transform. A plurality offrequencies and associated amplitudes are identified for each of thetransformed digital blocks and a subset of the identified amplitudes isselected for each of the digital blocks using a primary mask from a key.Message information is selected from a message using a transformationtable generated with a convolution mask. The chosen message informationis encoded into each of the transformed digital blocks by altering theselected amplitudes based on the selected message information.

[0021] With these and other advantages and features of the inventionthat will become hereinafter apparent, the nature of the invention maybe more clearly understood by reference to the following detaileddescription of the invention, the appended claims and to the severaldrawings attached herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a block flow diagram of a method for encoding digitalinformation according to an embodiment of the present invention.

[0023]FIG. 2 is a block flow diagram of a method for descaling digitalinformation according to an embodiment of the present invention.

[0024]FIG. 3 is a block flow diagram of a method for decoding digitalinformation according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0025] In accordance with an embodiment of the present invention,multiple transforms are used with respect to secure digitalwatermarking. There are two approaches to watermarking usingfrequency-domain or spatial domain transformations: using small blocksor using the entire data-set. For time-based media, such as audio orvideo, it is only practical to work in small pieces, since the entirefile can be many megabytes in size. For still images, however, the filesare usually much smaller and can be transformed in a single operation.The two approaches each have their own strengths. Block-based methodsare resistant to cropping. Cropping is the cutting out or removal ofportions of the signal. Since the data is stored in small pieces, a cropmerely means the loss of a few pieces. As long as enough blocks remainto decode a single, complete watermark, the crop does not remove themark. Block-based systems, however, are susceptible to scaling. Scaling,such as affine scaling or “shrinking,” leads to a loss of the highfrequencies of the signal. If the block size is 32 samples and the datais scaled by 200%, the relevant data now covers 64 samples. However, thedecoder still thinks that the data is in 32 samples, and therefore onlyuses half the space necessary to properly read the watermark. Whole-setapproaches have the opposite behavior. They are very good at survivingscaling, since they approach the data as a whole, and generally scalethe data to a particular size before encoding. Even a small crop,however, can throw off the alignment of the transform and obscure thewatermark.

[0026] With the present invention, and by incorporation of previouslydisclosed material, it is now possible to authenticate an image or songor video with the encoding key/key pair, eliminating false positivematches with cryptography and providing for the communication of acopyright through registration with third party authorities, instead ofthe original unwatermarked copy.

[0027] The present invention provides an obvious improvement over theprior art while improving on previous disclosures by offsettingcoordinate values of the original signal onto the key, which are thensubsequently used to perform decode or detection operations by the useror authorized “key-holder.” This offsetting is necessary with contentwhich may have a watermark “payload,” the amount of data that maysuccessfully be encoded, based on Shannon's noisy channel codingtheorem, that prevents enough invisible “saturation” of the signal withwatermark messages to afford the owner the ability to detect a singlemessage. An example, it is entirely possible that some images may onlyhave enough of a payload to carry a single 100 bit message, or 12 ASCIIcharacters. In audio implementations tested by the present inventor,1000 bits per second are inaudibly encoded in a 16 bit 44.1 kHz audiosignal. Most electronically available images do not have enough data toafford similar “payload” rates. Thus the premise that simultaneouscropping and scaling survival is more difficult for images than acomparable commercially available audio or video track. The addedsecurity benefit is that the more limited randomizer of a watermarkingsystem based on spread spectrum or frequency-only applications, therandom value of the watermark data “hopping ” over a limited signalingband, is that the key is also an independent source of ciphered orrandom data used to more effectively encode in a random manner. The keymay actually have random values larger than the watermark messageitself, measured in bits. The watermark decoder is assured that theimage is in its original scale, and can decide whether it has beencropped based on its “de-scaled” dimensions.

[0028] The benefits of a system requiring keys for watermarking contentand validating the distribution of said content is obvious. Differentkeys may be used to encode different information while secure one wayhash functions, digital signatures, or even one-time pads may beincorporated in the key to secure the embedded signal and affordnonrepudiation and validation of the watermarked image and “its” key/keypair. Subsequently, these same keys may be used to later validate theembedded digital signature only, or fully decode the digital watermarkmessage. Publishers can easily stipulate that content not only bedigitally watermarked, but that distributors must check the validity ofthe watermarks by performing digital signature checks with keys thatlack any other functionality.

[0029] Some discussion of secure digital watermarking has begun toappear. Leighton describes a means to prevent collusion attacks indigital watermarks in U.S. Pat. No. 5,664,018. Leighton, however, maynot actually provide the security described. For example, inparticularly instances where the watermarking technique is linear, the“insertion envelope” or “watermarking space” is well-defined and thussusceptible to attacks less sophisticated than collusion by unauthorizedparties. Over encoding at the watermarking encoding level is but onesimple attack in such linear implementations. Another considerationignored by Leighton is that commercially-valuable content in many casesmay already exist in a unwatermarked form somewhere, easily accessibleto potential pirates, gutting the need for any type of collusiveactivity. Such examples as compact disc or digitally broadcast videoabound. Digitally signing the embedded signal with preprocessing ofwatermark data is more likely to prevent successful collusion. Dependingon the media to be watermarked, highly granular watermarking algorithmsare far more likely to successfully encode at a level below anythingobservable given quantization artifacts, common in all digitally-sampledmedia, than expectations that a baseline watermark has anyfunctionality.

[0030] Furthermore, a “baseline” watermark as disclosed is quitesubjective. It is simply described elsewhere in the art as the“perceptually significant” regions of a signal: so making a watermarkingfunction less linear or inverting the insertion of watermarks would seemto provide the same benefit without the additional work required tocreate a “baseline” watermark. Indeed, watermarking algorithms shouldalready be capable of defining a target insertion envelope or regionwithout additional steps. Further, earlier disclosed applications by thepresent invention's inventor describe watermarking techniques that canbe set to encode fewer bits than the available watermarking region's“bit-space” or encoding unrelated random noise in addition to watermarkdata to confuse possible collusive or other attempts at erasure. Theregion of “candidate bits” can be defined by any number of compressionschemes or transformations, and the need to encode all of the bits issimply unnecessary. What is evident is that Leighton does not allow forinitial prevention of attacks on an embedded watermark as the content isvisibly or audibly unchanged. Moreover, encoding all of the bits mayactually act as a security weakness to those who can replicate theregions with a knowledge of the encoding scheme. Again, security mustalso be offset outside of the actual watermark message to provide atruly robust and secure watermark implementation.

[0031] In contrast, the present invention may be implemented with avariety of cryptographic protocols to increase both confidence andsecurity in the underlying system. A predetermined key is described as aset of masks. These masks may include primary, convolution and messagedelimiters but may extend into additional domains such as digitalsignatures of the message. In previous disclosures, the functionality ofthese masks is defined solely for mapping. Public and private keys maybe used as key pairs to further increase the unlikeliness that a key maybe compromised. Prior to encoding, the masks described above aregenerated by a cryptographically secure random generation process. Ablock cipher, such as DES, in combination with a sufficiently randomseed value emulates a cryptographically secure random bit generator.These keys will be saved along with information matching them to thesample stream in question in a database for use in descrambling andsubsequent detection or decode operation.

[0032] These same cryptographic protocols can be combined withembodiments of the present invention in administering streamed contentthat requires authorized keys to correctly display or play said streamedcontent in an unscrambled manner. As with digital watermarking,symmetric or asymmetric public key pairs may be used in a variety ofimplementations. Additionally, the need for certification authorities tomaintain authentic key-pairs becomes a consideration for greatersecurity beyond symmetric key implementations, where transmissionsecurity is a concern.

[0033] The following describes a sample embodiment of a system thatprotects digital information according to the present invention.Referring now in detail to the drawings wherein like parts aredesignated by like reference numerals throughout, there is illustratedin FIG. 1 a block flow diagram of a method for encoding digitalinformation according to an embodiment of the present invention. Animage is processed by “blocks,” each block being, for example, a 32×32pixel region in a single color channel. At step 110, each block istransformed into the frequency domain using a spectral transform or aFast Fourier Transform (FFT). The largest 32 amplitudes are identifiedand a subset of these 32 are selected using the primary mask from thekey at steps 120 and 130. One message bit is then encoded into eachblock at steps 140 and 150. The bit is chosen from the message using atransformation table generated using the convolution mask. If the bit istrue, the selected amplitudes are reduced by a user defined strengthfraction. If the bit is false, the amplitudes are unchanged.

[0034] Each of the selected amplitudes and frequencies are stored in thekey. After all of the image has been processed, a diagonal stripe ofpixels is saved in the key. This stripe can, for example, start in theupper left corner and proceed at a 45 degree angle through the image.The original dimensions of the image are also stored in the key.

[0035]FIG. 2 is a block flow diagram of a method for descaling digitalinformation according to an embodiment of the present invention. When animage is chosen to be decoded, it first is checked to determine if ithas been cropped and/or scaled. If so, the image is scaled to theoriginal dimensions at step 210. The resulting “stripe,” or diagonalline of pixels, is fit against the stripe stored in the key at step 220.If the fit is better than the previous best fit, the scale is saved atsteps 230 and 240. If desired, the image can be padded with, forexample, a single row or column of zero pixels at step 260 and theprocess can be repeated to see if the fit improves.

[0036] If a perfect fit is found at step 250, the process concludes. Ifno perfect fit is found, the process continues up to a crop “radius” setby the user. For example, if the crop radius is 4 the image can bepadded up to 4 rows and/or 4 columns. The best fit is chosen and theimage is restored to its original dimension, with any cropped areareplaced by zeroes.

[0037] Once the in formation has been descaled, it can be decodedaccording to an embodiment of the present invention shown in FIG. 3.Decoding is the inverse process of encoding. The decoded amplitudes arecompared with the ones stored in the key in order to determine theposition of the encoded bit at steps 310 and 320. The message isassembled using the reverse transformation table at step 330. At step340, the message is then hashed and the hash is compared with the hashof the original message. The original hash had been stored in the keyduring encoding. If the hashes match, the message is declared valid andpresented to the user at step 350.

[0038] Although various embodiments are specifically illustrated anddescribed herein, it will be appreciated that modifications andvariations of the present invention are covered by the above teachingsand within the purview of the appended claims without departing from thespirit and intended scope of the invention. Moreover, similar operationshave been applied to audio and video content for time-basedmanipulations of the signal as well as amplitude and pitch operations.The ability to descale or otherwise quickly determine differencingwithout use of the unwatermarked original is inherently important forsecure digital watermarking. It is also necessary to ensurenonrepudiation and third part authentication as digitized content isexchanged over networks.

What is claimed is:
 1. A method for encoding a message into digitalinformation, the digital information including a plurality of digitalblocks, comprising the steps of: transforming each of the digital blocksinto the frequency domain using a fast Fourier transform; identifying aplurality of frequencies and associated amplitudes for each of thetransformed digital blocks; selecting a subset of the identifiedamplitudes for each of the digital blocks using a primary mask from akey; choosing message information from the message using atransformation table generated with a convolution mask; and encoding thechosen message information into each of said transformed digital blocksby altering the selected amplitudes based on the chosen messageinformation.
 2. A method for encoding a message into digitalinformation, the digital information including a plurality of digitalblocks, comprising the steps of: transforming each of the digital blocksinto the frequency domain using a spectral transform; identifying aplurality of frequencies and associated amplitudes for each of thetransformed digital blocks; selecting a subset of the identifiedamplitudes for each of the digital blocks using a primary mask from akey; choosing message information from the message using atransformation table generated with a convolution mask; and encoding thechosen message information into each of said transformed digital blocksby altering the selected amplitudes based on the chosen messageinformation.
 3. The method of claim 1 , wherein the digital informationcontains pixels in a plurality of color channels forming an image, andeach of the digital blocks represents a pixel region in one of the colorchannels.
 4. The method of claim 2 , wherein the digital informationcontains audio information.
 5. The method of claim 1 , wherein said stepof identifying comprises: identifying a predetermined number ofamplitudes having the largest values for each of the transformed digitalblocks.
 6. The method of claim 1 , wherein the chosen messageinformation is a message bit and wherein said step of encoding comprisesthe step of: encoding the chosen message bit into each of saidtransformed digital blocks by reducing the selected amplitudes using astrength fraction if the message bit is true, and not reducing theselected amplitudes if the message bit is false.
 7. The method of claim6 , wherein the strength fraction is user defined.
 8. The method ofclaim 1 , further comprising the step of storing each of the selectedamplitudes and associated frequencies in the key.
 9. The method of claim1 , further comprising the step of storing a reference subset of thedigital information into the key.
 10. The method of claim 1 , whereinthe digital information contains pixels forming an image, furthercomprising the steps of: saving a reference subset of the pixels in thekey; and storing original dimensions of the image in the key.
 11. Themethod of claim 2 , wherein the digital information contains audioinformation, further comprising the steps of: saving a reference subsetof audio information in the key; and storing original dimensions of theaudio signal in the key.
 12. The method of claim 10 , wherein thereference subset of pixels form a line of pixels in the image.
 13. Themethod of claim 11 , wherein the reference subset of audio informationincludes an amplitude setting.
 14. The method of claim 8 , wherein theimage is a rectangle and the reference subset of pixels form a diagonalof the rectangle.
 15. The method of claim 1 , further comprising thestep of: requiring a predetermined key to decode the encoded messageinformation.
 16. The method of claim 1 , further comprising the step of:requiring a public key pair to decode the encoded message information.17. The method of claim 1 , further comprising the steps of: calculatingan original hash value for the message; and storing the original hashvalue in the key.
 18. A method for descaling a digital image using akey, comprising the steps of: determining original dimensions of thedigital image from the key; scaling the digital image to the originaldimensions; obtaining a reference subset of pixels from the key; andcomparing the reference subset of pixels with corresponding pixels inthe scaled digital image.
 19. A method for descaling audio digitalinformation using a key, comprising the steps of: determining originaldimensions of the audio digital information from the key; scaling theaudio digital information to the original dimensions; obtaining areference subset of audio information from the key; and comparing thereference subset of audio information with corresponding information inthe scaled audio information.
 20. The method of claim 18 , wherein saidstep of comparing determines a first fit value based on the comparison,and wherein the method further comprises the steps of: padding thescaled digital image with an area of pad pixels; and re-comparing thereference subset of pixels with corresponding pixels in the padded imageto determine a second fit value.
 21. The method of claim 20 , whereinthe area of pad pixels is a row of single pixels.
 22. The method ofclaim 20 , wherein the area of pad pixels is a column of single pixels.23. The method of claim 20 , wherein said steps of padding andre-comparing are performed a predetermined number of times.
 24. Themethod of claim 20 , further comprising the step of choosing a best fitvalue among the determined fit values and restoring the digital image tothe original size, including any pad pixels associated with the best fitvalue.
 25. The method of claim 14 , wherein said steps of padding andre-comparing are performed until a satisfactory fit value is obtained.26. A method of extracting a message from encoded digital informationusing a predetermined key, comprising the steps of: decoding the encodeddigital information into digital information, including a plurality ofdigital blocks, using the predetermined key; transforming each of thedigital blocks into the frequency domain using a fast Fourier transform;identifying a plurality of frequencies and associated amplitudes foreach of the transformed digital blocks; selecting a subset of theidentified amplitudes for each of the transformed digital blocks using aprimary mask from the key; comparing the selected amplitudes withoriginal amplitudes stored in the predetermined key to determine theposition of encoded message information; and assembling the messageusing the encoded message information and a reverse transformationtable.
 27. A method of extracting a message from encoded digitalinformation using a predetermined key, comprising the steps of: decodingthe encoded digital information into digital information, including aplurality of digital blocks, using the predetermined key; transformingeach of the digital blocks into the frequency domain using a spectraltransform; identifying a plurality of frequencies and associatedamplitudes for each of the transformed digital blocks; selecting asubset of the identified amplitudes for each of the transformed digitalblocks using a primary mask from the key; comparing the selectedamplitudes with original amplitudes stored in the predetermined key todetermine the position of encoded message information; and assemblingthe message using the encoded message information and a reversetransformation table.
 28. The method of claim 26 , further comprisingthe steps of: calculating a hash value for the assembled message; andcomparing the calculated hash value with an original hash value in thepredetermined key.
 29. A method for descaling a digital signal using akey, comprising the steps of: determining original dimensions of thedigital signal from the key; scaling the digital signal to the originaldimensions; obtaining a reference signal portion from the key; andcomparing the reference signal portion with a corresponding signalportion in the scaled signal.
 30. A method for protecting a digitalsignal comprising the step of: creating a predetermined key comprised ofa transfer function-based mask set and offset coordinate values of theoriginal digital signal; and encoding the digital signal using thepredetermined key.
 31. The method of claim 30 , wherein the digitalsignal represents a continuous analog waveform.
 32. The method of claim30 , wherein the predetermined key comprises a plurality of mask sets.33. The method of claim 30 , wherein the mask set is ciphered by a keypair comprising a public key and a private key.
 34. The method of claim30 , further comprising the step of: using a digital watermarkingtechnique to encode information that identifies ownership, use, or otherinformation about the digital signal, into the digital signal.
 35. Themethod of claim 30 , wherein the digital signal represents a stillimage, audio or video.
 36. The method of claim 30 , further comprisingthe steps of: selecting the mask set, including one or more masks havingrandom or pseudo-random series of bits; and validating the mask set atthe start of the transfer function-based mask set.
 37. The method ofclaim 36 , wherein said step of validating comprises the step of:comparing a hash value computed at the start of the transferfunction-based mask set with a determined transfer function of the hashvalue.
 38. The method of claim 36 , wherein said step of validatingcomprises the step of: comparing a digital signature at the start of thetransfer function-based mask set with a determined transfer function ofthe digital signature.
 39. The method of claim 36 , further comprisingthe step of: using a digital watermarking technique to embed informationthat identifies ownership, use, or other information about the digitalsignal, into the digital signal; and wherein said step of validating isdependent on validation of the embedded information.
 40. The method ofclaim 30 , further comprising the step of: computing a secure one wayhash function of carrier signal data in the digital signal, wherein thehash function is insensitive to changes introduced into the carriersignal for the purpose of carrying the transfer function-based mask set.41. A method for protecting a digital signal, comprising the steps of:creating a predetermined key comprised of a transfer function-based maskset and offset coordinate values of the original digital signal;authenticating the predetermined key containing the correct transferfunction-based mask set during playback of the data; and metering theplayback of the data to monitor content.
 42. The method of claim 30 ,wherein the digital signal is a bit stream and further comprising thesteps of: generating a plurality of mask sets to be used for encoding,including a random primary mask, a random convolution mask and a randomstart of message delimiter; obtaining a transfer function to beimplemented; generating a message bit stream to be encoded; loading themessage bit stream, a stega-cipher map truth table, the primary mask,the convolution mask and the start of message delimiter into memory;initializing the state of a primary mask index, a convolution maskindex, and a message bit index; and setting a message size equal to thetotal number of bits in the message bit stream.
 43. The method of claim30 , wherein the digital signal is a bit stream and further comprisingthe steps of: generating a mask set to be used for encoding, the setincluding a random primary mask, a random convolution mask, and a randomstart of message delimiter; obtaining a message to be encoded;compressing and encrypting the message if desired; generating a messagebit stream to be encoded; loading the message bit stream, a stega-ciphermap truth table, the primary mask, the convolution mask and the start ofmessage delimiter into memory; initializing the state of a primary maskindex, a convolution mask index, and a message bit index; and settingthe message size equal to the total number of bits in the message bitstream.
 44. The method of claim 42 wherein the digital information has aplurality of windows, further comprising the steps of: calculating overwhich windows in the sample stream the message will be encoded;computing a secure one way hash function of the information in thecalculated windows, the hash function generating hash values insensitiveto changes in the samples induced by a stega-cipher; and encoding thecomputed hash values in an encoded stream of data.
 45. The method ofclaim 36 , wherein said step of selecting comprises the steps of:collecting a series of random bits derived from keyboard latencyintervals in random typing; processing the initial series of random bitsthrough an MD5 algorithm; using the results of the MD5 processing toseed a triple-DES encryption loop; cycling through the triple-DESencryption loop, extracting the least significant bit of each resultafter each cycle; and concatenating the triple-DES output bits into therandom series of bits.